1. Field of the Invention
This invention relates to a control circuit for driving a stepping motor which is suitable for use, for example, in a magnetic disc storage unit.
2. Prior Art
There has been proposed a disc storage unit in which a seek operation to move the heads to the desired cylinder is performed by means of a stepping motor. And, it is known in the art that the stepping motor can be controlled by a control circuit in such a manner that the rotor thereof is accelerated and decelerated in accordance with a predetermined unique speed pattern previously stored in an associated memory. However, such a conventional motor control circuit suffers from a deficiency that the rotor steps out when the supply voltage to the stepping motor becomes greater or less than the nominal value by a certain amount, since the stepping motor is driven in accordance with the same speed pattern regardless of the variation of the supply voltage.